I think the barriers to getting ZFS into OS-X were probably legal, not technical ones. There's long history of the CDDL tripping up reasonable attempts to use Z

I think the barriers to getting ZFS into OS-X were probably legal, not technical ones. There's long history of the CDDL tripping up reasonable attempts to use ZFS and I doubt Apple would have wanted to proceed without approval and/or alternate licensing. Likewise Oracle has no real reason to let them do that without writing a check with lots of zeros on it. There's also a decent chunk of what ZFS supports (particularly flexible volume pool management) that would be useless on almost every machine that Apple makes and sells. Your example of pulling a drive out of one machine and putting it in another is either impossible (soldered-on storage) or highly unlikely (user-serviceable SSD, but hidden behind a bunch of pentalobe screws) with their modern hardware lineup.